The present invention relates to the detection of specific nucleic acid sequences in a target test sample.
In particular, the present invention relates to the automated detection of specific nucleic acid sequences which are either unamplified or amplified nucleic acid sequences (amplicons).
In addition, the present invention relates to the use of automated amplification, methods and compositions for monitoring successful amplification, improved methods for reducing the chance for contamination, and the use of unified reaction buffers and unit dose aliquots of reaction components for amplification.
Finally, the present invention also relates to unique constructs and methods for the conventional or automated detection of one, or more than one different nucleic acid sequences in a single assay.
The development of techniques for the manipulation of nucleic acids, the amplification of such nucleic acids when necessary, and the subsequent detection of specific sequences of nucleic acids or amplicons has generated extremely sensitive and nucleic acid sequence specific assays for the diagnosis of disease and/or identification of pathogenic organisms in a test sample.
Amplification of Nucleic Acids
When necessary, enzymatic amplification of nucleic acid sequences will enhance the ability to detect such nucleic acid sequences. Generally, the currently known amplification schemes can be broadly grouped into two classes based on whether, the enzymatic amplification reactions are driven by continuous cycling of the temperature between the denaturation temperature, the primer annealing temperature, and the amplicon (product of enzymatic amplification of nucleic acid) synthesis temperature, or whether the temperature is kept constant throughout the enzymatic amplification process (isothermal amplification). Typical cycling nucleic acid amplification technologies (thermocycling) are polymerase chain reaction (PCR), and ligase chain reaction (LCR). Specific protocols for such reactions are discussed in, for example, Short Protocols in Molecular Biology 2nd Edition, A Compendium of Methods from Current Protocols in Molecular Biology, (Eds. Ausubel et al., John Wiley and Sons, New York, 1992) chapter 15. Reactions which are isothermal include: transcription-mediated amplification (TMA), nucleic acid sequence-based amplification (NASBA), and strand displacement amplification (SDA).
U.S. Patent documents which discuss nucleic acid amplification include U.S. Pat. No. 4,683,195; 4,683,202; 5,130,238; 4,876,187; 5,030,557; 5,399,491; 5,409,818; 5,485,184; 5,409,818; 5,554,517; 5,437,990 and 5,554,516 (each of which are hereby incorporated by reference in their entirety). It is well known that methods such as those described in these patents permit the amplification and detection of nucleic acids without requiring cloning, and are responsible for the most sensitive assays for nucleic acid sequences. However, it is equally well recognized that along with the sensitivity of detection possible with nucleic acid amplification, the ease of contamination by minute amounts of unwanted exogenous nucleic acid sequences is extremely great. Contamination by unwanted exogenous DNA or RNA nucleic acids is equally likely. The utility of amplification reactions will be enhanced by methods to control the introduction of unwanted exogenous nucleic acids and other contaminants.
Prior to the discovery of thermostable enzymes, methods that used thermocycling were made extremely difficult by the requirement for the addition of fresh enzyme after each denaturation step, since initially the elevated temperatures required for denaturation also inactivated the polymerases. Once thermostable enzymes were discovered, cycling nucleic acid amplification became a far more simplified procedure where the addition of enzyme was only needed at the beginning of the reaction. Thus reaction tubes did not need to be opened and new enzyme did not need to be added during the reaction, allowed for an improvement in efficiency and accuracy as the risk of contamination was reduced, and the cost of enzymes was also reduced. An example of a thermostable enzyme is the polymerase isolated from the organism Thermophilus aquaticus. 
In general, isothermal amplification can require the combined activity of multiple enzyme activities for which no optimal thermostable variants have been described. The initial step of an amplification reaction will usually require denaturation of the nucleic acid target, for example in the TMA reaction, the initial denaturation step is usually xe2x89xa765xc2x0 C., but can be typically xe2x89xa795xc2x0 C., and is used when required to remove the secondary structure of the target nucleic acid.
The reaction mixture is then cooled to a lower temperature which allows for primer annealing, and is the optimal reaction temperature for the combined activities of the amplification enzymes. For example, in TMA the enzymes are generally a T7 RNA polymerase and a reverse transcriptase (which includes endogenous RNase H activity). The temperature of the reaction is kept constant through out the subsequent isothermal amplification cycle.
Because of the lack of suitable thermostable enzymes, some isothermal amplifications will generally require the addition of enzymes to the reaction mixture after denaturation at high temperature, and cool-down to a lower temperature. This requirement is inconvenient, and requires the opening of the amplification reaction tube, which introduces a major opportunity for contamination.
Thus, it would be most useful if such reactions could be more easily performed with a reduced risk of contamination by methods which would allow for integrated denaturation and amplification without the need for manual enzyme transfer.
Amplification Buffer and Single Reaction Aliquot of Reagents
Typical reaction protocols require the use of several different buffers, tailored to optimize the activity of the particular enzyme being used at certain steps in the reaction, or for optimal resuspension of reaction components. For example, while a typical PCR 10xc3x97 amplification buffer will contain 500 mM KCl and 100 mM Tris HCl, pH 8.4, the concentration of MgCl2 will depend upon the nucleic acid target sequence and primer set of interest. Reverse transcription buffer (5xc3x97) typically contains 400 mM Tris-Cl, pH 8.2; 400 mM KCl and 300 mM MgCl2, whereas Murine Maloney Leukemia Virus reverse transcriptase buffer (5xc3x97) typically contains 250 mM Tris-Cl, pH 8.3; 375 mM KCl; 50 mM DTT (Dithiothreitol) and 15 mM MgCl2.
While such reaction buffers can be prepared in bulk from stock chemicals, most commercially available amplification products provide bulk packaged reagents and specific buffers for use with the amplification protocol. For example, commercially available manual amplification assays for detection of clinically significant pathogens (for example Gen-Probe Inc. Chlamydia, and Mycobacterium tuberculosis detection assays) requires several manual manipulations to perform the assay, including dilution of the test sample in a sample dilution buffer (SDB), combination of the diluted sample with amplification reaction reagents such as oligonucleotides and specific oligonucleotide promoter/primers which have been reconstituted in an amplification reconstitution buffer (ARB), and finally, the addition to this reaction mixture of enzymes reconstituted in an enzyme dilution buffer (EDB).
The preparation and use of multiple buffers which requires multiple manual additions to the reaction mixture introduces a greater chance for contamination. It would be most useful to have a single unified buffer which could be used in all phases of an amplification protocol. In particular, with the commercially available TMA assays described above, the requirement for three buffers greatly complicates automation of such a protocol.
Bulk packaging of the enzyme or other reaction components by manufacturers, may require reconstitution of the components in large quantities, and the use of stock amounts of multiple reagents, can be wasteful when less than the maximal number of reactions are to be carried out, as some of these components may be stable for only a short time. This process of reconstitution also requires multiple manipulations by the user of the stock reagents, and aliquoting of individual reaction amounts of reagents from stocks which creates a major opportunity for contamination.
Methods and compositions for the preparation of bulk quantities of preserved proteins are known, see for example, U.S. Pat. No. 5,098,893; 4,762,857; 4,457,916; 4,891,319; 5,026,566 and International Patent Publications WO 89/06542; WO 93/00806; WO 95/33488 and WO 89/00012, all of which are hereby incorporated by reference in their entirety. However, the use of pre-aliquoted and preserved reagent components in single reaction quantities/dose is both very useful and economical. Single aliquots of enzyme reagent avoids multiple use of bulk reagents, reducing waste, and greatly reducing the chance of contamination. Further, such single reaction aliquots are most suitable for the automation of the reaction process.
The requirement for many changes of buffer and the multiple addition of reagents complicates the automation of such reactions. A single dose unit of reaction buffer mixture, and a unified combination buffer will both simplify automation of the process and reduce the chance of contamination.
Automation of Nucleic Acid Detection with or without Amplification
Nucleic acid probe assays, and combination amplification/probe assays can be rapid, sensitive, highly specific, and usually require precise handling in order to minimize contamination with non-specific nucleic acids, and are thus prime candidates for automation. As with conventional nucleic acid detection protocols, it is generally required to utilize a detection probe oligonucleotide sequence which is linked by some means to a detectable signal generating component. One possible probe detection system is described in U.S. Pat. No. 4,581,333 hereby incorporated by reference in its entirety.
In addition, automation of a nucleic acid detection system targeting unamplified or amplified nucleic acid, or a combined automated amplification/detection system will generally be adaptable to the use of nucleic acid capture oligonucleotides that are attached to some form of solid support system. Examples of such attachment and methods for attachment of nucleic acid to solid support are found in U.S. Pat. Nos. 5,489,653 and 5,510,084 both of which are hereby incorporated by reference.
Automation of amplification, detection, and a combination of amplification and detection is desirable to reduce the requirement of multiple user interactions with the assay. Apparatus and methods for optically analyzing test materials are described for example in U.S. Pat. No. 5,122,284 (hereby incorporated by reference in its entirety). Automation is generally believed to be more economical, efficient, reproducible and accurate for the processing of clinical assays. Thus with the superior sensitivity and specificity of nucleic acid detection assays, the use of amplification of nucleic acid sequences, and automation at one or more phases of a assay protocol can enhance the utility of the assay protocol and its utility in a clinical setting.
Advantage of Internal Control Sequences
Nucleic acid amplification is highly sensitive to reaction conditions, and the failure to amplify and/or detect any specific nucleic acid sequences in a sample may be due to error in the amplification process as much as being due to absence of desired target sequence. Amplification reactions are notoriously sensitive to reaction conditions and have generally required including control reactions with known nucleic acid target and primers in separate reaction vessels treated at the same time. However, internal control sequences added into the test reaction mixture would truly control for the success of the amplification process in the subject test reaction mixture and would be most useful. U.S. Pat. No. 5,457,027 (hereby incorporated by reference in its entirety) teaches certain internal control sequences which are useful as an internal oligonucleotide standard in isothermal amplification reactions for Mycobacterium tuberculosis. 
However it would be extremely useful to have a general method of generating internal control sequences, that would be useful as internal controls of the various amplification procedures, which are specifically tailored to be unaffected by the nucleic acid sequences present in the target organism, the host organism, or nucleic acids present in the normal flora or in the environment. Generally, such internal control sequences should not be substantially similar to any nucleic acid sequences present in a clinical setting including human, pathogenic organism, normal flora organisms, or environmental organisms which could interfere with the amplification and detection of the internal control sequences.
Detection of More than one Nucleic Acid Sequence in a Single Assay
In general, a single assay reaction for the detection of nucleic acid sequences is limited to the detection of a single target nucleic acid sequence. This single target limitation increases costs and time required to perform clinical diagnostic assays and verification control reactions. The detection of more than one nucleic acid sequence in a sample using a single assay would greatly enhance the efficiency of sample analysis and would be of a great economic benefit by reducing costs, for example helping to reduce the need for multiple clinical assays.
Multiple analyte detection in a single assay has been applied to antibody detection of analyte as in for example International Patent Publication number WO 89/00290 and WO 93/21346 both of which are hereby incorporated by reference in their entirety.
In addition to reducing cost, time required, the detection of more than one nucleic acid target sequence in a single assay would reduce the chance of erroneous results. In particular multiple detection would greatly enhance the utility and benefit using internal control sequences and allow for the rapid validation of negative results.
The present invention comprises methods for the automated isothermal amplification and detection of a specific nucleic acid in a test sample to be tested comprising:
a) combining a test sample to be tested with a buffer, a mixture of free nucleotides, specific oligonucleotide primers, and optionally thermostable nucleic acid polymerization enzyme, in a first reaction vessel and placing the reaction vessel in an automated apparatus such that;
b) the automated apparatus heats the first reaction vessel to a temperature, and for a time sufficient to denature, if necessary, the nucleic acid in the sample to be tested;
c) the automated apparatus cools the first reaction vessel to a temperature such that oligonucleotide primers can specifically anneal to the target nucleic acid;
d) the automated apparatus transfers the reaction mixture from the first reaction vessel to a second reaction vessel, and brings the reaction mixture in contact with thermolabile nucleic acid amplification enzyme;
e) the automated apparatus maintains the temperature of the second reaction vessel at a temperature which allows primer mediated amplification of the nucleic acid;
f) the automated apparatus contacts the amplified nucleic acid in the second reaction vessel with a capture nucleic acid specific for the nucleic acid to be tested such that they form a specifically-bound nucleic acid-capture probe complex;
g) the automated apparatus optionally washes the specifically captured amplified nucleic acid such that non-specifically bound nucleic acid is washed away from the specifically-bound nucleic acid-capture probe complex;
h) the automated apparatus contacts the specifically-bound nucleic acid-capture probe complex with a labeled nucleic acid probe specific for the amplified nucleic acid such that a complex is formed between the specifically amplified nucleic acid and the labeled nucleic acid probe;
i) the automated apparatus washes the specifically-bound nucleic acid-capture probe-labeled probe complex such that non-specifically bound labeled probe nucleic acid is washed away from the specifically bound complex;
j) the automated apparatus contacts the specifically bound complex with a solution wherein an detection reaction between the labeled nucleic acid probe is effected between the solution and the label attached to the nucleic acid such that a detectable signal is generated from the sample in proportion the amount of specifically-bound amplified nucleic acid in the sample;
wherein the steps h, i, and j may occur sequentially or simultaneously;
k) the automated apparatus detects the signal and optionally displays a value for the signal, or optionally records a value for the signal.
As used herein, the term test sample includes samples taken from living patients, from non-living patients, from surfaces, gas, vacuum or liquids, from tissues, bodily fluids, swabs from body surfaces or cavities, and any similar source. The term buffer as used here encompasses suitable formulations of buffer which can support the effective activity of a label, for example an enzyme placed into such buffer when treated at the appropriate temperature for activity and given the proper enzymatic substrate and templates as needed. The term specific oligonucleotide nucleic acid primers means an oligonucleotide having a nucleic acid sequence which is substantially complementary to and will specifically hybridize/anneal to a target nucleic acid of interest and may optionally contain a promoter sequence recognized by RNA polymerase. The term reaction vessel means a container in which a chemical reaction can be performed and preferably capable of withstanding temperatures of anywhere from about xe2x88x9280xc2x0 C. to 100xc2x0 C.
The instant invention further provides for the method described above, wherein the reaction buffer is a unified buffer and as such is suitable for denaturation nucleic acids and annealing of nucleic acids, and is further capable of sustaining the enzymatic activity of nucleic acid polymerization and amplification enzyme. Further encompassed by the invention is the method wherein the nucleic acid amplification enzyme is administered in the second reaction chamber as a single assay dose amount in a lyophilized pellet, and the reaction chamber is sealed prior to the amplification step.
The invention teaches an apparatus for the automated detection of more than one nucleic acid target sequences or amplicons comprising a solid phase receptacle (SPR(copyright) pipet-like devise) coated with at least two distinct zones of a capture nucleic acid oligonucleotide.
The invention teaches a method for the automated detection of more than one nucleic acid target sequence comprising contacting a solid phase receptacle (SPR(copyright) pipet-like devise) coated with at least two distinct capture nucleic acid oligonucleotides in a single or multiple zones to a sample to be tested and detecting a signal(s) from specifically bound probe. In one embodiment of the invention, the SPR(copyright) is coated with two distinct zones of capture nucleic acid oligonucleotides which are specific for different nucleic acid sequence targets. In another embodiment of the invention, the SPRY is coated with at least one capture probe for a target nucleic acid sequence, and one capture probe for an amplification control nucleic acid sequence which when detected confirms that amplification did take place.
The present invention also comprises an internal amplification positive control nucleic acid having the nucleic acid sequence of RIC1 and a second internal amplification positive control nucleic acid having the nucleic acid sequence of RIC2.
The present invention further comprises a method for generating an internal amplification positive control nucleic acid consisting of:
generating random nucleic acid sequences of at least 10 nucleotides in length, screening said random nucleic acid sequence and selecting for specific functionality, combining in tandem a number of such functionally selected nucleic acid sequences, and screening the combined nucleic acid sequence and optionally selecting against formation of intra-strand nucleic acid dimers, or the formation of hairpin structures.